LightLevel sensor: update state when config changes.
LightLevel sensor: update state when config changes.

Re-compute `state.dark` and `state.daylight` when `config.tholddark` or
`config.tholdoffset` has changed (issue #173).

dresden-elektronik/deconz-rest-plugin,dresden-elektronik/deconz-rest-plugin,dresden-elektronik/deconz-rest-plugin,dresden-elektronik/deconz-rest-plugin,dresden-elektronik/deconz-rest-plugin